[noselasd]

That's not particularly relevant, you're thinking at the wrong layer. Seen from a program sitting on top of TCP, there's no such thing as a TCP message/block. You can very well grab a single 16MB chunk with 1 read() call, if the socket buffer is sized for that.

Or you can append incoming data to a big internal buffer which you pass through decompression once that buffer fills up.

You would have to look at protocols sitting above TCP that transfers compressed data, that typically would define a message based protocol, and how an implementation decompresses that data.